Stannous salts such as stannous fluoride are used in dentifrices as agents for preventing plaque. However, some disadvantages of stannous salts include instability, tendency to stain teeth, astringency and unpleasant taste for users. For that reason, oral care compositions containing stannous salts such as stannous fluoride are often presented as dual phase compositions, in which the stannous salt is kept separate from the other components in order to reduce its negative effects on the oral cavity, such as astringency and unpleasant taste. See, e.g., U.S. Pat. No. 6,521,216 and U.S. Pat. No. 7,063,833, both to Glandorf et al.
Sodium tripolyphosphate is an effective anticalculus (anti-tartar) agent, but the compound is not generally compatible with stannous salts in long term storage (such as that normally sustained in the lifetime of a tube of toothpaste between time of packaging and time of discard after use). In particular, the combination of sodium tripolyphosphate with stannous salts such as stannous fluoride can lead to undesirable stannous tripolyphosphate intermediates.
Accordingly, there is an ongoing need for oral care compositions that have improved efficacy in combating plaque and tooth discoloration and are still able to retain long-term stability.